There are numerous applications in the electric power industry where medium power switching devices are needed. Various electromechanical relays, contactors and manually operated selector and control switches are often used. Often such devices are limited in their applications to new demands of electric power systems.
For example, conventional manually operated rotary switches easily provide a large number of electrical poles and positions sometimes required for power switching but are not designed to operate at high speed and often not by means of remote control. Known electromechanical relay and contactors can be operated remotely at high speeds but provide only few contacts when used in medium power switching as from 5 to 30 amps. Often complicated and multiplied switching devices are used in complicated schemes which can add to cost and reduce reliability of power control systems.